ElectrolysisHigher Tier

Higher Tier: Half Equations for Aqueous Electrolysis

Part of Electrolysis of Aqueous Solutions · GCSE GCSE Chemistry revision

This higher tier covers Higher Tier: Half Equations for Aqueous Electrolysis within Electrolysis of Aqueous Solutions for GCSE Chemistry. Revise Electrolysis of Aqueous Solutions in Electrolysis for GCSE Chemistry with 21 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 7 of 13 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.

Topic position

Section 7 of 13

Practice

21 questions

Recall

15 flashcards

🎓 Higher Tier: Half Equations for Aqueous Electrolysis

At Higher Tier, you are expected to write and balance half equations for all four possible products in aqueous electrolysis:

Cathode (reduction — gain of electrons):

Hydrogen: 2H⁺ + 2e⁻ → H₂
Copper: Cu²⁺ + 2e⁻ → Cu

Anode (oxidation — loss of electrons):

Chlorine: 2Cl⁻ → Cl₂ + 2e⁻
Oxygen: 4OH⁻ → O₂ + 2H₂O + 4e⁻

The oxygen half equation is the most complex — notice that 4 OH⁻ ions produce 1 O₂ molecule and 2 H₂O molecules. Check: 4 oxygens on each side ✓, 4 hydrogens on each side ✓, 4 negative charges = 4 electrons lost ✓.

Keep building this topic

Read this section alongside the surrounding pages in Electrolysis of Aqueous Solutions. That gives you the full topic sequence instead of a single isolated revision point.

Key Facts to Memorise Common Misconceptions The Water Complication Electrolysis of Brine — Click to Explore

Practice Questions for Electrolysis of Aqueous Solutions

When sodium chloride (NaCl) is dissolved in water, which four types of ion are present in the solution?

A. Na⁺, Cl⁻, H⁺ and OH⁻
B. Na⁺, Cl⁻, H₂O and OH⁻
C. Na⁺, Cl⁻ only
D. Na⁺, Cl⁻, H₂ and O²⁻

1 markfoundation

Describe the three products formed when concentrated brine is electrolysed, and state where each is produced.

3 marksstandard

Quick Recall Flashcards

State the anode rule for aqueous electrolysis.

If a halide ion (Cl⁻, Br⁻, or I⁻) is present → the halogen gas forms. If NO halide is present → oxygen gas forms from the OH⁻ ions. Example: Cl⁻ present → Cl₂ forms. SO₄²⁻ present (no halide) → O₂ forms.

State the cathode rule for aqueous electrolysis.

If the metal is MORE reactive than hydrogen (above H in reactivity series) → hydrogen gas forms. If the metal is LESS reactive than hydrogen (below H) → the metal deposits. Examples: Na above H → H₂ forms. Cu below H → Cu deposits.

21 questions on Electrolysis of Aqueous Solutions — practise free

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Key Facts to Memorise

Common Misconceptions